This disclosure relates generally to semiconductor manufacturing and more particularly to a method of manufacturing a capacitor and a metal gate on a semiconductor device.
In the semiconductor industry, metal-oxide semiconductor (MOS) transistors have typically been formed using polysilicon gate electrodes. Polysilicon material has been preferred due to its thermal resistive properties during high temperature processing, which allows it to be annealed at high temperatures along with the source and drain regions. Furthermore, polysilicon's ability to block the ion implantation of doping atoms into the channel region is advantageous, as it allows for the easy formation of self aligned source and drain structures after gate patterning is completed.
However, polysilicon gate electrodes suffer from certain disadvantages. Polysilicon gate electrodes are formed from semiconductor materials that have relatively high resistivity compared to most metal materials. This causes the polysilicon gate electrode to operate at a slower speeds compared to a gate electrode made of a metal material. To compensate for the high resistance and corresponding lower operation speed, the polysilicon materials often require extensive and expensive silicide processing in order to increase their speed of operation to an acceptable level.
Another disadvantage to using polysilicon gate electrodes is the polysilicon depletion effect. This occurs because polysilicon can presently only be doped to a range of about 2×1020 cm3 to about 3×1020 cm3. Ideally, a doping concentration of at least 5×1021 cm3 is desired in the gate material. Because of the doping limit, when a polysilicon gate is biased, a depletion region near the polysilicon gate and gate dielectric interface is generated due to the lack of carriers.
Therefore, it is desirable to replace the polysilicon gate electrode with a metal gate electrode. The problem then arises of how to integrate capacitor fabrication with the metal gate process while achieving a cost competitive process.
Accordingly, it would be desirable to provide a method of manufacturing a capacitor and a metal gate on a semiconductor device absent the disadvantages discussed above.